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| United States Patent |
5,246,469
|
|
Arfelli
, et al.
|
September 21, 1993
|
Fuel stabilization
Abstract
Distillate fuel is stabilized against degradation during storage by
inserting into storage tanks solid materials containing polar sites to
enable polar condensation of the fuel constituents active in degradation.
Polyether or polyester polyurethane open cell foams are the prime solid
stabilizers proposed.
| Inventors:
|
Arfelli; William (Avondale Heights, AU);
Power; Alan (Keilor, AU);
Solly; Richard (Ascot Vale, AU)
|
| Assignee:
|
The Commonwealth of Australia (Canberra, AU)
|
| Appl. No.:
|
183188 |
| Filed:
|
February 29, 1988 |
| PCT Filed:
|
July 24, 1987
|
| PCT NO:
|
PCT/AU87/00235
|
| 371 Date:
|
February 29, 1988
|
| 102(e) Date:
|
February 29, 1988
|
| PCT PUB.NO.:
|
WO88/00914 |
| PCT PUB. Date:
|
February 11, 1988 |
Foreign Application Priority Data
| Current U.S. Class: |
44/384; 44/389; 44/417; 44/418; 44/419; 585/2; 585/3; 585/4; 585/823; 585/824; 585/830 |
| Intern'l Class: |
C10L 001/30; C10L 001/16 |
| Field of Search: |
44/51,384
585/2,3,4,823,824,830
|
References Cited
U.S. Patent Documents
| 2306870 | Dec., 1942 | Engelhardt | 44/51.
|
| 4032510 | Jun., 1977 | Floyd et al. | 585/2.
|
| 4339246 | Jul., 1982 | Yamamura et al. | 44/51.
|
| 4659334 | Apr., 1987 | Matlach | 44/51.
|
| Foreign Patent Documents |
| 1341693 | Dec., 1973 | GB.
| |
Primary Examiner: McAvoy; Ellen M.
Attorney, Agent or Firm: Roylance, Abrams, Berdo & Goodman
Claims
The claims defining the invention are as follows: We claim:
1. A method for minimizing the chemical degradation of a liquid hydrocarbon
distillate fuel during storage for an extended period of time,
said liquid hydrocarbon distillate fuel containing cracked products derived
from a heavy crude or distillation fraction, said cracked products
including chemically unstable species that promote fuel degradation upon
storage for an extended period of time leading to a build-up of insoluble
particulate material,
comprising the step of
storing said hydrocarbon fuel in contact with a polymeric solid which is
capable of removing or counteracting fuel components catalyzing or
participating in degradation reactions and which is selected from the
group consisting of polyurethane foam, polyolefin fiber,
polyacrylonitrile, cotton, wool, and polyacetate,
whereby the amount of said chemically unstable species in said liquid
hydrocarbon fuel is reduced.
2. The method according to claim 1, wherein the polymeric solid is in the
form of cellular foam, sponge, mesh, woven fabric, naturally entwined or
bound fiber bundles, surface coatings, strips, films, or solids
encapsulated in a fuel-permeable container.
3. The method according to claim 1, wherein the polymeric solid is an
open-cell polyurethane foam.
4. The method according to claim 1, wherein the polymeric solid is a
polyether-based polyurethane foam.
5. The method according to claim 1, wherein the polymeric solid is a
polyester-based polyurethane foam and the liquid hydrocarbon fuel contains
aromatic hydrocarbons.
6. The method according to claim 1, wherein the polymeric solid is a
polyurethane foam based on poly(diethylene glycol) adipate or
poly(oxypropyl) poly(oxyethyl) glycerol or on an acrylonitrile-styrene
modified polyoxyalkylene polyether resin.
7. The method according to claim 1, wherein the polymeric solid is a
polyethylene cloth containing heteroatom functional groups or polar
additives.
8. The method according to claim 1, wherein the polymeric solid is
poly(1,4-phenylene terephthalamide) cloth.
9. The method according to claim 1, wherein the polymeric solid is a
polyurethane foam and the method of storing the hydrocarbon fuel in
contact with the polymeric solid is by adding the polymeric solid to a
storage tank containing the fuel in an amount of 1 to 5 grams of
polyurethane foam per liter of fuel.
10. A method for minimizing the chemical degradation of a liquid
hydrocarbon distillate fuel during storage for an extended period of time,
said liquid hydrocarbon distillate fuel containing cracked products derived
from a heavy crude or distillation fraction, said cracked products
including chemically unstable species that promote fuel degradation upon
storage for an extended period of time leading to a build-up of insoluble
particulate material,
comprising the step of
contacting said hydrocarbon fuel with a polymeric solid which is capable of
removing or counteracting fuel components catalyzing or participating in
degradation reactions and which is selected from the group consisting of
polyurethane foam, polyolefin incorporating a polar copolymer, polyamide,
Nylon 6--6, polyester fiber, polyacrylonitrile, cotton, wool, and
polyacetate,
whereby the amount of said chemically unstable species in said liquid
hydrocarbon fuel is reduced.
Description
This invention relates to a method and means of preventing degradation in
liquid hydrocarbon fuels.
Some liquid fuels particularly distillates are stored in static storages
for periods of up to several years.
Over extended periods of time, small but significant changes in fuel
properties can occur. Important properties which change with time are
colour and insolubles content. Insoluble materials can plug fuel system
filters, reduce or alter the fuel flow through engine nozzles and form
sludges in the fuel tanks. Formation of insolubles is an indication of
chemical reactions in a fuel. Chemical degradation of fuels is an
important aspect of fuel stability.
Storage stability of distillate fuels has been of modest concern for fuels
made by refining processes based on straight run distillation. However,
increasing quantities of heavy crudes and distillation fractions are being
run in refineries using cracking processes to increase the yield of middle
distillate fuels. The cracked products, which contain chemically unstable
species, are blended into straight run streams. The unstable components,
although diluted by the blending, still exert a strong influence on
insoluble material formation, particularly for long storage periods.
Stabilizing additives have been proposed to reduce the extent of insoluble
material formation in middle distillate fuels. Specific additives, such as
phenylenediamines and hindered phenols, have been used. These additives
have been found to be effective in preventing the formation of gums in
gasolines and peroxides in jet fuels. They have been shown to be
ineffective in preventing the formation of particulate matter in
distillate fuels.
Additive manufacturers' experience with diesel fuels and home heating oils
has led them to recommend alkyl amines as stability additives. These
effective additives contained alkyl amines, some in conjunction with a
metal deactivator (MDA). These observations were made on several straight
run distillates as well as 30% blend of catalytically cracked stock (light
cycle oil--LCO) in a stable straight run fuel.
U.S. Pat. No. 3,701,641 proposes to stabilise distillate fuels against
degradation using a polyamine having 2 to 6 amino groups and 25 to 50
carbon atoms.
Cyclohexylamines have been proposed as distillate fuel stabilizers in U.S.
Pat. Nos. 3,640,692, 3,336,124 and 4,040,799 and in French Patent 1441717.
It is an object of this invention to provide a simple alternative means to
stabilizing fuels.
To this end the present invention provides a method of stabilizing liquid
hydrocarbon fuels which comprises storing the fuel with solids capable of
removing from fuel those active elements which catalyse or participate in
the degradation reactions.
These insoluble solid additives reduce the amount of fuel degradation
material which is suspended in the fuel or deposited on the walls of the
container. The solid additives useful in this invention are thought to
contain polar sites to enable polar condensation of the active
constituents to occur. A solid additive with this capability acts as a
preferred deposition site for molecules of insoluble material, and for
precursors of insoluble material in the fuel. These precursors are
partitioned between the solid additive and the fuel molecules. Reduction
of the concentration of these precursors in the fuel reduces degradation
of the fuel.
Application of solid additives to the interior of fuel system components
for fuel stabilization can be in the form of cellular foams, sponges,
mesh, woven fabric, naturally entwined or bound fibre bundles, surface
coatings, strips, films, or solids such as powders or particulate material
encapsulated in fuel permeable containers. Preferred foams are open cell
polyurethane foams or polymeric foams including urea, carbamate, ester or
amide groups available as polar sites.
Polyurethane (PU) foam is a solid which possesses high fuel stabilization
performance when immersed in fuel during storage. These polymers comprise
large numbers of well defined polar functional groups which have affinity
for unstable components in the fuel. The partition of unstable precursors
between solid and fuel strongly favours their depletion from the fuel to
the foam.
Fuel degradation material is also deposited on the foam surface, rather
than forming as suspended particulate matter in the fuel.
When polyurethane foams are employed it is generally preferred to use
polyether based polyurethanes because of their greater stability in
avoiding degradation by hydrolysis but in some cases polyester based
polyurethanes will be quite suitable due to their better stability in
fuels containing higher levels of aromatic hydrocarbons.
The method of this invention can be carried out either as a pre-storage
treatment or by inserting the foams into storage tanks. Generally the
foams are present in a concentration of at least 0.01% weight by volume
with a preferred concentration of 1 to 5 g. per litre of fuel.
By passing the fuel through a bed of solids as taught by this invention or
through an open cell foam, the stability of the fuel is improved and its
storage life extended. This is particularly useful with distillates which
are highly susceptible to degradation.
Generally however it is preferred to incorporate the solids or foams into
fuel storage tanks. The foams are preferably open cell in structure and
have a porosity which ensures that the volume of fuel displaced is low but
still provides a large surface area for fuel contact.
A number of comparison tests of accelerated ageing of distillate fuels have
been carried out to quantify the fuel stabilizing effect of a wide range
of PU foam samples.
The test results are illustrated in FIGS. 1 to 5 which in graph form,
provide comparisons between fuel ageing in the presence of a range of
foams listed in table 1 and compared in FIGS. 1 to 3 with reference fuel
samples while FIGS. 4 and 5 illustrate the effect of PU foams on fuels
containing fuel deposit promoters.
TABLE 1
______________________________________
PU Foam Cell Polyol Air Flow
No* Type Type Code (m.sup.3 /h)
______________________________________
#1 .sup. C.sup.a
Ether PE850 .sup. N.D..sup.c
#2 .sup. R.sup.b
Ester ME020 N.D
#3 R Ester ME010 38.1
#4 R Ester ME015 40.9
#5 C Ester EF430 0.5
#6 C Ether PE900 2.5
#7 C Ether HR940 8.0
#8 R Ester ME020 N.D.
#9 R Ester ME030 26.4
#10 R Ester SFI N.D.
#11 R Ester SFII N.D.
#12 R Ester SFIII N.D
#13 R Ether SFIV N.D.
______________________________________
Classification of PU Foams used in Fuel Stabilization Experiments.
.sup.a C = closedcell foam structure
.sup.b R = reticulated (opencell) structure
.sup.c N.D. = not determined
*Foams #1-9 were manufactured by Cable Makers Australia
Foams #10-13 were manufactured by Scotfoam, U.S.A.
The polyester foams 2, 3, 4, 8 & 9 contain modified poly(diethylene
glycol)adipate with a density of 28 kg/m.sup.3 and a cell count of 5 to 30
pores perlinear centimetre.
The polyether foams 1,5,6 & 7 contain poly(oxypropyl)
poly(oxyethyl) glycerol and have a density of 27 kg/m.sup.3 and 15 to 25
pores per linear centimetre.
Foam 13 contains an acrylonitrile-styrene modified polyoxyalkylene
polyether resins.
A range of polyether and polyester PU foams were tested as stabilizing
additives for (light cycle oil/straight run distillate) fuel blends during
storage for various time intervals, in the temperature range
43.degree.-120.degree. C. Intervals of storage at ambient temperature,
approximately equivalent to specific experimental accelerated fuel
stressing conditions used in this work, were calculated to be as follows:
______________________________________
Fuel Stress Ambient Temperature
(Temp - Time)
Equivalent (Years)
______________________________________
43.degree. C. -
6 months 2.0
65.degree. C. -
43 days 2.3
80.degree. C. -
13 days 1.9
80.degree. C. -
14 days 2.0
120.degree. C. -
72 hours 6.9
120.degree. C. -
96 hours 9.2
______________________________________
FIGS. 1, 2, 4 and 5 show the amounts of total insolubles formed from the
same fuel blend during fuel ageing for five different time intervals at
three different temperatures.
In all fuel stressing trials, duplicate samples of the respective fuel
blends without additives were carried through all procedures, for
comparison with duplicate sample blends containing additives. In some
experiments, known fuel destabilizing agents (deposit promoters) were
added in conjunction with PU foam additives in order to determine the
efficiency of PU foam in counteracting the effects of these agents on fuel
stability.
The degree of degradation of fuel blends under the various experimental
conditions was determined by measurements of parameters considered to be
relevant to fuel instability :
______________________________________
(i) Particulate matter
= Total Insolubles (mq/1)
(ii) Adherent Gum
(iii)
Filtration Index
(iv) Colour (ASTM D1500)
______________________________________
Where applicable, changes in mass of the PU foam additives after ageing
were also measured. Soluble gum concentrations, by ASTM D381, have been
shown to have only a tenuous link 10 with quantitative measurements of
fuel instability.
The Filtration Index [(iii) above] is the ratio by which the filtration
time (sec) of an aged fuel, with or without additive, exceeded the
filtration time (sec) of the prefiltered, unaged fuel blend, under a
standardized method of pressure filtration (29 kPa; 4.2 p.s.i.) through
Whatman No.540 cellulose fibre membranes with nominal pore size of 8.0
micron. For the filtered, unaged reference fuel, replicate determinations
showed good reproducibility (.+-.5%), with the average filtration time
being 90 sec. For the aged fuels, however, reproducibility of filtratation
times for some duplicate samples was not as good as for the unaged fuel.
Factors such as formation of variable-sized particulate matter during
ageing of duplicate samples, and non-uniformity in peformance of the
nominal pore size filter membranes with filtration of contaminated
liquids, may have contributed to variations, sometimes as much as .+-.20%,
for aged fuel duplicates. In most cases, however, variations were
<.+-.10%.
Filtration times for aged-fuel duplicates were averaged and converted into
the above Filtration Index for semi-quantitative filterability evaluation.
Aged fuels with Filtration Index between 1.0 and 1.3 were considered to
have "good" filtration characteristics, between 1.3 and 2.0 "fair", and
greater than 2.0 were considered "poor".
Mild accelerated ageing of fuels at 43.degree. C. is widely accepted as
being the most realistic and accurate test for estimation of the long term
stability of diesel distillates during bulk storage. The data in FIG. 1,
therefore, are considered to be representative of the performance of PU
foam fuel stabilizing additives under field conditions Ageing at
43.degree. C. generally requires relatively long trial periods (at least
13 weeks) for significant changes in the fuel to occur. The data in the
FIG. 1 was obtained after 26 weeks fuel ageing at this temperature, a
period equivalent to about two years ambient storage.
The effectiveness of the PU foams for fuel stabilization is clearly
demonstrated in FIG. 1. Total insolubles and particulate levels were very
low, close to experimental detection limits for those parameters,
indicating very high fuel stability compared to the aged reference fuel
Polyether foam #1 underwent slight physical disintegration during
protracted fuel immersion, with visible foam cell fragments contributing
to the particulate components, thus increasing total insolubles. This
foam, however, was the only foam in this trial which was not designed
specifically for fuel immersion. The latter group showed unaffected
structural integrity.
Filtration Index values (FIG. 1) for all fuels aged with PU foams indicated
"good" filterability, equivalent to, or approaching that for the clean,
unaged reference fuel (1.0). The aged reference fuel had a significantly
higher Filtration Index of 1.6.
Improvement in colour of aged fuel blends in presence of PU foams was
greatest for ageing periods less than the equivalent of 6 months at
ambient temperature.
Colour differences between fuel containing PU foams and aged reference fuel
decreased as the period of ageing increased.
Greater colour stability of aged fuel was achieved when the foam/fuel
weight/volume ratio was of the order of 5 g per litre. Foams #9, #14, #15
and #16 (Table 2) were effective in suppressing colour degradation
compared to the reference fuel after ageing for periods of up to 48 hours
at 120.degree. C. (equivalent of 4.6 years storage at ambient
temperature). The ageing period is shown in hours in Table 2. The fuels
aged with foam, which showed improved colour stability, also had greatly
reduced formation of insolubles and improved filterability as seen in
Table 2.
TABLE 2
__________________________________________________________________________
Insolubles
Filtration
Foam
Foam Foam
Colour
Colour
Colour
mg/L Index
No. Type g/L 15 hrs
39 hrs
48 hrs
48 hrs
48 hrs
__________________________________________________________________________
NONE -- 4.0 5.0 5.0 21 4.8
#9 ME030
3.8 3.0 3.5 3.5 2 1.1
#14 SFV 4.8 2.0 2.0 2.5 3 1.0
#15 SFVI 5.6 2.5 2.5 2.5 2 1.2
#16 SFVII
5.1 2.5 2.5 2.5 2 1.1
__________________________________________________________________________
Foam #9 was manufactured by Cable Makers Australia, and Foams #14, #15 an
#16 by Scottfoam, USA.
Colour was determined by ASTM DE1500. The colour of the unaged fuel was
2.0.
Very low levels of total insolubles, combined with good filtration
characteristics and colour stability are properties not normally
associated with aged distillates which contain 30% unhydrotreated LCO. The
above data, therefore, demonstrate that fuel-immersible PU foams exert a
strong stabilizing influence on distillate fuel.
Under the experimental fuel ageing conditions shown in FIGS. 2 and 3, each
of the PU foam samples selected for evaluation imparted significant
improvement to fuel stability. The level of total insolubles was reduced
in almost all cases by more than 50%, generally by more than 70%, and in
some cases by greater than 80%.
FIGS. 2 and 3 also show no apparent discrimination between polyether or
polyester PU foams with respect to their fuel stabilizing properties at
the experimental fuel foam ratios.
The physical form of the foams possibly exerted a small influence on fuel
stabilization efficiency. Foams 2, 3 and 4 were reticulated (open cell)
types with high permeability to gases (air flow >30 m.sup.3 h.sup.-1) and
therefore, presumably, to liquids. Each of these foam samples gave at
least a 75% reduction in total insolubles, compared to the reference fuel.
Foams 1, 5, 6 and 7 were closed cell PU foams. Total insolubles reductions
for foams 1, 6 and 7 were comparable to those of the reticulated foams;
however, foam #5 (FIG. 3), which had a much lower air flow (0.51 m.sup.3
h.sup.-1), gave a relatively poor reduction (55%) in total insolubles. The
low permeability of this foam may have reduced free access of fuel to the
interior of the sample during ageing, lowering overall fuel/foam contact,
thus affecting its fuel stabilizing influence. It may be noted that
difficulty was experienced in removing residual fuel from this sample,
even after hexane rinsing, and heating (115.degree. C.) in a vacuum oven.
This also was attributed to the very low permeability of the foam.
Ageing of the fuel blend in the presence of foams #1 and #2 (FIG. 2)
clearly had a beneficial effect on aged fuel filterability. Filtration
Index values for the 80.degree. C.--13 day fuel stress data for the foams
are in the "good" to "fair" categories, while the reference fuel
Filtration Index indicates "poor" filterability. Similar results were
obtained for the 120.degree. C. data, even though for foam #1, the
particulate measurement was boosted by foam fragments from thermal
decomposition of the foam.
Filtration Index values shown in FIG. 3, however, indicate "poor"
filterability for all fuel samples, whether aged with or without added PU
foams. Particulate levels were much lower for fuels aged in the presence
of foams, but their filter blocking tendencies appear to be worse than for
the reference fuel. The two sets of filtration data in FIGS. 3 and 4
cannot be compared directly, since different fuel stressing conditions
were used. It has been observed previously that filtration characteristics
of fuels can be worse after shorter term than longer term ageing at the
same temperature. This may be related to changes in particle sizes of fuel
deposits with time.
The performance of PU foams 1 and 2 for fuel stabilization was compared
with that of fuel soluble additives FOA-3 and FOA-15 (FIG. 2). In a
previous study, using a similar fuel blend, reductions in total insolubles
in the range 50-70% were achieved when FOA-3 was added at a concentration
of 24 ppm. At the same concentration, this additive effected reductions in
total insolubles of 55% for the fuel blend used in the present study, a
result significantly lower than that achieved with the immersed PU foams
(>80% reduction). The Filtration Index was also quite high in comparison.
The FOA-15 additive, however, gave total insolubles reduction comparable to
those effected by the PU foams, although the Filtration Index of 1.9 was
significantly higher. This may have been due to the presence of the
dispersant component in FOA-15, which has been demonstrated previously to
adversely affect aged fuel filterability. It was concluded from this study
that the PU foams were at least as effective as these fuel-soluble
additives in suppressing distillate fuel degradation during ageing.
The effectiveness of PU foam as a fuel stabilization additive was examined
using fuel blend doped with known deposit promoters thiophenol,
chloroacetic acid and copper naphthenate.
Addition of thiophenol to the fuel blend, at concentrations of 0.001M and
0.003M, caused increases in total insolubles from 43 mg/l, for the undoped
fuel, to 217 and 600 mg/l, respectively, during fuel ageing at 65.degree.
C. for 43 days (FIG. 4). Very large increases in adherent gum levels were
observed; the very low relative levels of particulate matter (2 mg/l, or
less) were consistent with Filtration Index values which indicated "good"
filterability. Thus, filterability evaluation in this case was not an
indication of actual fuel stability.
Dramatic reductions in total insolubles were achieved when PU foam samples
were immersed in the solutions of thiophenol in the fuel (FIG. 4). The
magnitude of insolubles reduction (>98%) indicated that the powerful
deposit promoting activity of thiophenol had been completely counteracted
by the PU foam additive.
Filtration Index values of the fuel aged with the thiophenol/foam
combination rated "good" in the filterability classification.
It may be seen from FIG. 4 that similar results were obtained using
solutions of chloroacetic acid (0.001M and 0.003M) in the fuel blend.
Respective increases in total insolubles of 2.4 and 3.6 fold at the two
acid concentrations were not as large as those for thiophenol solutions
(5.0 and 14.0 fold). Immersed PU foam additives effectively counteracted
the destabilizing effect of the chloroacetic acid, although not quite to
the same degree observed for the thiophenol solutions. The acid had a much
greater tendency than the thiol to increase the proportion of particulate
matter, relative to adherent gum, and this was reflected in the "poor"
filterability rating for fuel aged with acid alone. In combination with PU
foam additive, particulate was reduced by >80% for the acid/fuel
solutions, and improved Filtration Index values were observed (2.6:1.1 for
0.001M solution, 2.6:1.8 for 0.003M solution).
Addition of copper (as copper naphthenate) to the reference blend at a
concentration of 0.25 mg/l caused an increase in total insolubles from 39
mg/l (with no additive) to 70 mg/l, during ageing at 80.degree. C. for 13
days (FIG. 5). The catalytic effect of copper in promoting deposit
formation was not enhanced when the copper concentration was increased to
1.00 mg/l. The ratio of particulate to adherent gum which formed in the
presence of copper was about 4:1, compared to about 2:1 for chloroacetic
acid, again much greater than that for thiophenol. Filtration Index values
for the fuel aged with copper present did not increase, relative to the
aged reference fuel.
Ageing of the 0.25 mg/l solution of copper in fuel with PU foam additive
decreased total insolubles formation by 89%. The actual amount of total
insolubles formed (8 mg/l) was the same as when the reference fuel (with
no copper added ) was aged with PU foam, indicating that the deposit
forming action of the copper had been fully counteracted by the foam. With
the 1.00 mg/l copper solution, the foam was slightly less effective,
giving an 81% reduction in insolubles. However, the excellent performance
of PU foam as a copper deactivator is evident. Significant improvements in
Filtration Index values were also achieved when the copper solutions were
aged with PU foam samples (FIG. 5).
Polyolefin solids which are capable of acting as preferred deposition sites
for molecules of insoluble material, and which possess an affinity for
precursors of insoluble material in fuel, showed fuel stabilization
properties. The active sites arise from heteroatom functional groups or
the addition of polar additives such as Ciba-Geigy Tinuvin 770, Tinuvin
622 and Chimassorb 944.
Knitted high density polyethylene cloth, impregnated with 0.45 weight
percent of polymeric hindered amine light stabilizers containing
2,2,6,6-tetramethylpiperidine moieties (Tinuvin 622 and Chimassorb 944)
were immersed for 12 days at 80.degree. C. in a fuel blend similar to that
described above. Total insolubles were 11 mg/l, compared to 58 mg/l for
the fuel aged with no additive, a reduction of 81%. Filtration Index
values for these aged fuel samples were 1.6 and 4.5, respectively.
Polypropylene, and high and low density polyethylene without the polar
copolymer additives were ineffective as fuel stabilizers, giving no
reduction in total insolubles compared to the reference fuel in the above
experiments.
Thus, the use of polyolefin solids, in conjunction with polar copolymers,
has been successfully demonstrated for fuel stabilization.
Woven Kevlar [poly(1,4-phenylene terephthalamide)] cloth, nylon 6--6 cord
and polyester fibres showed fuel stabilization properties when immersed in
the test fuel (14 days, 80.degree. C.) containing 0.001 mol/l chloroacetic
acid (deposit promotor). The reference fuel without additive produced 97
mg/l of total insolubles whereas that produced in fuel aged in the
presence of the above materials were 45, 50 and 8 mg/l, respectively.
Synthetic and natural fibrous materials were found to be fuel stabilizers
with respect to fuel colour, before and after fuel ageing for 7 days at
80.degree. C. It can be seen from Table 3 that the fibrous materials
reduced fuel colour readings by 0.5-1.5, compared to the aged reference
fuel with no additive. Under controlled laboratory conditions of fuel
ageing, colour reductions of this order in comparative tests, using the
same fuel blend, indicate significant reductions in the amounts of
insoluble fuel degradation products. Evaluation of these solid additives
by this means has illustrated their effectiveness as fuel stabilizing
additives.
TABLE 3
______________________________________
Fibre Polar Chain Aged fuel
Trade Name
wt. Functional Colour (ASTM
of Fibre (g/l) Groups D1500).sup.a
______________________________________
DACRON 45
4.5 ESTER 3.0
ORLON 75 2.0 ACRYLONITRILE 3.0
NYLON 6-6
1.6 AMIDE 2.0
COTTON 1.9 HYDROXYL; ETHER 2.5
WOOL 1.7 AMIDE; CYSTINE 2.0
RAYON 3.8 ACETATE 3.0
(BLANK -- -- 3.5
FUEL)
______________________________________
.sup.a Initial fuel colour: 1.5
Fuel Stress: 80.degree. C., 7 days
This invention is applicable to all distillate fuel tanks, including static
storages, vehicle fuel tanks and aircraft fuel tanks.
Adoption of the present invention provides the following advantages:
(i) Insoluble solid additives possessing the properties described, when
inserted in fuel systems provide a continuously efficient, passive
environment for minimising the effects of fuel instability during storage.
(ii) Such solids have the capability of maximising storage stability of
very unstable fuels containing cracked refinery stock. This is
significant, since refineries world-wide are increasing the proportion of
cracked stock into middle distillates.
(iii) Less demand would be placed upon expensive refinery hydrotreating, or
the use of fuel stability additives, for fuel systems which incorporated
suitable solid additives.
(iv) Solids such as polyurethane foams, polyester fibre and Kevlar cloth
are stable and non-toxic to handle. No precautions are required in their
use. This may be contrasted with chemical additives, which are generally
toxic and require protective equipment to be handled in their concentrated
form.
It is envisaged that the fuel stabilizing system of this invention will
find the following application:
(a) For insertion in Defence fuel systems and strategic installations where
there is a requirement to protect fuel from chemical degradation (most
Defence materiel has this requirement).
(b) For use in vehicle fuel tanks in which the deterioration of distillate
fuel may occur due to chemical ageing. This includes commercial diesel
powered vehicles, diesel powered rural equipment and marine and air craft.
(c) For use in storage tanks of all sizes in which distillate fuel is kept
for any length of time, when degradation products are likely to increase
in concentration and cause malfunction in equipment when subsequently
used.
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